Narrated Abu Abdullah Al-nu'man Ibn Bashir (may Allah be pleased with him): 'I heard the Messenger of Allah (peace be upon him) say, "The legitimate is clear and the prohibited is clear and between them there are suspicious things which not many people know. He who avoids suspicious things will keep his religion and his honor clear and he who falls into suspicious things will be falling into the prohibited, like a shepherd who lets his flock graze around protected land and is about to enter it. [Beware] Each king has protected land. [Beware] Allah's protected land is the things which He has prohibited. [Beware] In the body is a lump which, if it is sound, the whole body is sound, and if it is corrupt, the whole body is corrupt -- that is the heart."'
[Bukhari and Muslim]

Narrated Abu Musa (may Allah be pleased with him): The Prophet (peace be upon him) said, "The example of one who remembers his Lord in comparison to the one who does not remember his Lord, is that of a living creature compared to a dead one."
[Bukhari]

Narrated Abu Malek Al-Hareth Ibn Assem Al-Ash'ari (may Allah be pleased with him), 'The Messenger of Allah (peace be upon him) said, "Cleanliness is part of faith and praising Allah fills the scale and glorifying and praising Allah fills what is between heaven and earth and prayer is light and charity is proof and endurance is illumination and the Quran is an evidence for or against you; every person starts his day and he is offering his soul for sale, thus liberating or imperishing it."'
[Muslim]

Narrated Abu Sa'id Al-Khudri (may Allah be pleased with him), 'I heard the Messenger of Allah (peace be upon him) say, "He of you who sees an abomination should change it with his hand; if he can not, then by his tongue; if he can not, then in his heart and that is the weakest of faith."'
[Muslim]